Add CHECK_GL and CHECK_GL_MEM

Our error detection is really bad right now in terms of the OpenGL API. This
formalizes our error detection.

We basically crash in all cases. I'm more or less OK with this.

Signed-off-by: Casey Dahlin <cdahlin@redhat.com>
Introduce colorbufs

With this we now have an abstraction over the framebuffer API and can easily
render to textures. A colorbuf is essentially just a vector of texmaps that can
be drawn to.

There's some hacks around the edges of where this landed: blank texmaps are no
longer compressed due to compressed textures not being writable, and we've
hardcoded the 800x600 resolution in a few places. The next few commits should
get things clean again.

Signed-off-by: Casey Dahlin <cdahlin@redhat.com>